Upon forming a PZT ferroelectric film having a perovskite structure by a gel-sol method typically represented by the CSD method, when a precursor film of a ferroelectric film which contains more Pb than the stoichiometric composition thereof is fired under a usual condition (for example, in an air atmosphere), a quasi-stable phase called a pyrochlore phase is formed. When this pyrochlore phase is remained, the PZT ferroelectric film having the perovskite structure cannot be obtained. For this reason, it has been known that in order to transform the pyrochlore phase to the perovskite phase, the firing has to be generally carried out at high temperature of 600 to 700° C.
In order to avoid this high-temperature firing, a method for producing a PZT film is disclosed wherein the method comprises a step of forming a precursor film by drying it at the temperature of 300° C. or lower after the liquid composition for forming the PZT ferroelectric film is applied to a substrate and a step of forming the perovskite phase by firing at low temperature in an oxidative atmosphere after a divalent lead ion (Pb2+) in the precursor film is reduced to a zero-valent lead (Pb0) so as to suppress formation of the pyrochlore phase (for example, see Patent Literature 1). This method is characterized by that the reduction is carried out by heating the substrate having the formed precursor film to 300 to 450° C. with the temperature rising rate of 5° C./minute or higher in a non-oxidative atmosphere, or the substrate having the formed precursor film is heated to 300 to 450° C. with the temperature rising rate of 5° C./second or higher in an oxidative atmosphere.
On the other hand, a method for forming the ferroelectric thin film is disclosed wherein after a sol-gel solution comprising a metal alkoxide and a solvent or a solution of a metal organic agent is applied to one surface of a supporting substrate, in an ozone-containing gas atmosphere UV rays are irradiated to a coat film comprising the sol-gel solution or the solution of a metal organic agent, and then, the supporting substrate is subject to a heat treatment, or UV rays are irradiated with simultaneous heat treatment of the supporting substrate (for example, see Patent Literature 2). In Patent Literature 2 in which production of a (BaxSr1-x)TiO3 film is explained, it is described that the same effect can also be obtained even when this method is used in production of other ferroelectric thin films such as PZT film and the PLZT film. In addition, in Patent Literature 2, it is described that because unnecessary compounds in the coat film can be effectively removed by a photochemical reaction with ozone, which is generated by interaction of a free radical or an excited molecule liberated from the coat film by irradiation of UV rays with an oxygen and UV rays, the formation method of the ferroelectric thin film having less inhibitory factors for crystal growth in the heat treatment process thereby having excellent electric characteristics can be realized.